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Its cells develop from the follicular cells surrounding the ovarian follicle. [5] The follicular theca cells luteinize into small luteal cells (thecal-lutein cells) and follicular granulosa cells luteinize into large luteal cells (granulosal-lutein cells) forming the corpus luteum. Progesterone is synthesized from cholesterol by both the large ...
At the end of the luteal phase, progesterone levels fall and the corpus luteum atrophies. The drop in progesterone leads to endometrial ischemia which will subsequently shed in the beginning of the next cycle at the start of menses. [1] This last stage in the luteal or secretory phase may be called the ischemic phase and lasts just for one or ...
Between menarche and menopause the ovaries regularly alternate between luteal and follicular phases during the monthly menstrual cycle. [9] Stimulated by gradually increasing amounts of estrogen in the follicular phase, discharges of blood flow stop and the uterine lining thickens. Follicles in the ovary begin developing under the influence of ...
Follicular phase diagram of hormones and their origins Follicle-stimulating hormone (FSH) is secreted by the anterior pituitary gland (Figure 2). FSH secretion begins to rise in the last few days of the previous menstrual cycle, [ 3 ] and is the highest and most important during the first week of the follicular phase [ 4 ] (Figure 1).
Note: Many sources misrepresent the pace of follicle growth, some even suggesting that it takes only fourteen days for a primordial follicle to become preovulatory. Actually, the follicular phase of the menstrual cycle means the time between selection of a tertiary follicle and its subsequent growth into a preovulatory follicle.
The follicular phase (or proliferative phase) is the phase of the menstrual cycle during which the ovarian follicles mature. The follicular phase lasts from the beginning of menstruation to the start of ovulation. [12] [13] For ovulation to be successful, the ovum must be supported by the corona radiata and cumulus oophorous granulosa cells. [14]
This bistability is most obvious in the transition between the follicular and luteal phases, and arises from interactions between positive and negative feedback loops involving GnRH, LH, FSH, estrogen, and progesterone. The kisspeptin system creates a switch-like mechanism driving the transition from negative to positive feedback.
While the normal human menstrual cycle typically lasts 4 weeks (28 days, range 24–35 days) and consists of a follicular phase, ovulation, and a luteal phase followed by either menstruation or pregnancy, the anovulatory cycle has cycle lengths of varying degrees.